If you've been involved with any kind of blockchain, I'm sure you're familiar with a blockchain fork. A forking is a process of copying an open sorce blockchain project and creating a new copy of the code. Some blockchains are open to public and some are not. For example, Bitcoin blockchain is open to public and anyone can start using it and become a part of the blockchain network. However, some chains are private or protected in a way so only certain people can use them.
We can categorize blockchain in three types based on their access levels.
Permissionless or public blockchain
In a permissionless or public blockchain, anyone can use public keys, anyone can be a node and join the network, and anyone can become a miner to service the network and see a reward. Anyone can read the chain, anyone can make changes, and anyone can add a new block, with the condition of following the blockchain rules. Bitcoin blockchain is an example of permissionless blockchain.
Public permissioned blockchain
In a public permissioned blockchain, a user needs permission from the starter of the blockchain to read the information on the blockchain, restrict who can transact on the blockchain, and who can serve the network by writing new block into the chain. Ripple and Hyperledger Fabric are permissioned blockchains.
Private permissioned blockchain
Blockchain technology is a secure, shared, public ledger. Public portion of the blockchain makes a blockchain available to anyone. What if businesses such as banks, hospitals, and government do not want to share data publicly but want to use blockchain technology? In such cases, a private blockchain is the solution. A private blockchain is developed within a private network or organization and available to limited people within a network.
Private permissioned blockchain are permissioned blockchain where data is not available for public to read but digital identities of participants are managed and monitored by a consortium or a regulatory authority for any other operations. Each participant in the blockchain has an access level that allows participants to do certain things on the blockchain.